This site presents the idea that birds developed from flying pterosaurs.
This is a credible alternative to the current, mainstream idea that birds developed from land-based dinosaurs.

Tuesday, February 7, 2017

Ontogeny and Phylogeny

Let's step back a bit and look at ontogeny (development) and phylogeny (evolution).
What are the different ways researchers have tried to relate ontogeny to phylogeny?
Some of the people involved: Meckel, Haeckel, von Baer, Gould.

The von Baer's lawis a concept in biology introduced by Karl Ernst von Baer to explain the details of embryo development.[1] He specifically aimed at rebutting the recapitulation theory introduced by Johann Friedrich Meckel in 1808. According to Meckel's theory, embryos pass through successive stages that represent the adult forms of less complex organisms in the course of development, and that ultimately reflects scala naturae (the great chain of being).[2] von Baer believed that such linear development is impossible. He posited that instead of linear progression, embryos started from one, or a few, basic forms that are similar for different animals, and then developed in a branching pattern into increasingly different looking organisms. Defending his ideas, he was also opposed to the theory of common ancestry and descent with modification as proposed by Charles Darwin in 1859, and particularly the revised recapitulation theory ("ontogeny recapitulates phylogeny") of Ernst Haeckel, a supporter of Darwin's theory in Germany.[3][4]

Gould's hope was to show that the relationship between ontogeny and phylogeny is fundamental to evolution, and at its heart is a simple premise—that variations in the timing and rate of development provide the raw material upon which natural selection can operate."[2]

Summary:Meckelembryos pass through successive stages that represent the adult forms of less complex organisms in the course of development, and that ultimately reflects scala naturae (the great chain of being)von Baerembryos started from one, or a few, basic forms that are similar for different animals, and then developed in a branching pattern into increasingly different looking organisms.Haeckelontogeny recapitulates phylogenyhttps://embryo.asu.edu/pages/ontogeny-and-phylogeny-1977-stephen-jay-gouldErnst Haeckel's theory of recapitulation, had an evolutionary perspective. Evolutionary recapitulation differed from other forms of recapitulation as it integrates the theory of common ancestry for all organisms. Gouldvariations in the timing and rate of development provide the raw material upon which natural selection can operate

Ontogeny is the developmental history of an organism within its own lifetime, as distinct from phylogeny, which refers to the evolutionary history of a species. In practice, writers on evolution often speak of species as "developing" traits or characteristics. This can be misleading. While developmental (i.e., ontogenetic) processes can influence subsequent evolutionary (e.g., phylogenetic) processes[1] (see evolutionary developmental biology), individual organisms develop (ontogeny), while species evolve (phylogeny).

In general, the polarities of developmental novelties
in the model are congruent with von Baer’s
rule—the hypothesis that stages that occur earlier
in development are phylogenetically more
broadly distributed and historically plesiomorphic
(e.g., Gould, ’77). However, the model does not rely
solely on relative timing of events in ontogeny to
justify these polarities. The stages of the model
are inferred from the hierarchical nature of the
developmental mechanisms of the follicle rather
than from an analysis of the ontogenetic progression
of plumages grown within the follicles of
birds. Thus, plumulaceous feathers (stage II) are
not primitive to pennaceous feathers (stage IIIa
and beyond) because the first plumage of extant
birds is usually downy, but because the simplest
differentiated follicle collar would have produced plumulaceous feathers.

One detail, however, of feather development appears to violate von Baer’s rule. During the development of the first feather papillae in the embryo (before day 12 in the chick, Gallus gallus), the barb ridge primordia appear as longitudinal condensations within the feather papillae before the follicle and collar are fully formed (Lucas and Stettenheim, ’72). However, this developmental event—the origin of the feather before the follicle and collar—is clearly derived because barb ridges would be unable to grow without the spatial organization provided by the collar.

The most important supporter of von Baer's law was Charles Darwin, who wrote in his Origin of Species:[The] adult [animal] differs from its embryo, owing to variations supervening at a not early age, and being inherited at a corresponding age. This process, whilst it leaves the embryo almost unaltered, continually adds, in the course of successive generations, more and more difference to the adult. Thus the embryo comes to be left as a sort of picture, preserved by nature, of the ancient and less modified condition of each animal. This view may be true, and yet it may never be capable of full proof.[9]

In terms of taxonomic hierarchy, characters in the embryo will be formed in the order, first from those of phylum, then class, order, family, genus, and finally species.[6]

Von Baer's second law states that embryos develop from a uniform and noncomplex structure into an increasingly complicated and diverse organism. For example, a defining and general characteristic of vertebrates is the vertebral column. This feature appears early in the embryonic development of vertebrates. However, other features that are more specific to groups within vertebrates, such as fur on mammals or scales on reptiles, form in a later developmental stage. Von Baer argued that this evidence supporting epigenetic development rather than development from preformed structures. He concluded from the first two laws that development occurs through epigenesis, when the complex form of an animal arises gradually from unformed material during development.

IMPORTANT

It is important to realize that the feather stages up to developmental Stage IIIa are ALREADY present in the actinofibrils of the pterosaur. In other words, there is no need to evolve those stages (in the transition to basal Paraves) because they are already present in the pterosaur ancestor.

3 comments:

https://benthamopen.com/contents/pdf/TOOENIJ/TOOENIJ-9-14.pdfAs I have noted many times [8], when birds such as ratites become secondarily terrestrial, they come to superficially resemble dinosaurs, and much confusion has resulted from this similitude

Humorous:https://benthamopen.com/contents/pdf/TOOENIJ/TOOENIJ-9-14.pdfOstrom’s own theory often made the case for a dinosaurian origin of birds from small coelurosaurs by stating that the Eichstättspecimen of Archaeopteryx was first misidentified as the small coelurosaurian Compsognathus! For Ostrom this errorwas proof of relatedness; although another specimen of Archaeopteryx was misidentified as a pterosaur

Note

This site presents the idea that pterosaurs (rather than dinosaurs) developed into birds. This is not an "evolutionism" vs. "creationism" issue.An "evolutionist" can say that the pterosaur to bird developments are due to neo-Darwinian means (random mutation and natural selection).On the other hand, a "creationist" can say that those developments are the acts of a higher intelligence.This site does not take a position on the "evolutionism" vs. "creationism" question.

Philosophy

Like most people, I have philosophical ideas that go beyond the nuts and bolts of the scientific analysis of the origin and development of birds.There are larger questions that philosophers have grappled with since the most ancient times. If anyone is interested in my take on those more philosophical ideas, click here.But please realize that all the ideas of this site are pure materialist, scientific ideas supported by physical evidence and scientific studies.

The 19th-century German philosopher Arthur Schopenhauer astutely summarized the three stages through which all truth passes: first, it is ridiculed; second, it is violently opposed;

and third, it is accepted as being self-evident.

"In the choice between changing one's mind and proving there's no need to do so, most people get busy on the proof."~John Kenneth Galbraith

Keywords

origin of birds, pterosaur is the ancestor of modern birds, birds did not evolve from dinosaurs, cladistics, stratocladistics, Cretaceous, Mesozoic, fossil record, BAD, BAND, birds are not dinosaurs, flightless birds, aves